In a conventional mixing operation to prepare an injection solution or an intravenous solution, aspirating a medicinal solution in a vial (medicinal solution container) into a syringe or injecting a medicinal solution in a syringe into a vial is manually carried out by an operator. In these processes, an injection needle attached to an edge of the syringe is punctured into a rubber cap of the vial so that the inside of the syringe and the vial form an enclosed space.
When the medicinal solution contained in the vial is aspirated into the syringe, a piston provided in the syringe is moved in a direction where the piston is pulled out from an outer tube. Internal pressure of the vial decreases with increasing amount of medicinal solution that was aspirated into the syringe, increasing a force required to drive the piston. When the injection needle is pulled out from the vial where the internal pressure is still low, ambient air possibly enters the vial due to a pressure difference between the internal pressure of the vial and the atmospheric pressure, generating air bubbles in the medicinal solution in the vial. It is difficult and time-consuming to extract the medicinal solution alone from the medicinal solution containing the air bubbles, significantly increasing an operation time and thereby making the operation very inefficient.
A conventional means to avoid such an overly low internal pressure of the vial is to aspirate the medicinal solution from the vial into the syringe while gradually replacing the medicinal solution of the vial with the air inside the syringe. As illustrated in FIG. 15, air 103 is aspirated into a syringe 101 beforehand, and an injection needle 106 attached to the syringe 101 is then punctured into a rubber cap 107 which seals a vial 102 so that a needle tip reaches below the liquid surface of a medicinal solution 104 in the vial 102. After that, a piston 108 is moved in a direction where the piston is pulled out from an outer tube 109 to aspirate the medicinal solution 104 into the syringe 101. When it is determined that the internal pressure of the vial 102, which decreases as the medicinal solution 104 is aspirated, reaches a given value, a positional relationship between the vial 102 and the syringe 101 illustrated in FIG. 15 is reversed to be upside down so that the tip of the injection needle 106 is above the liquid surface of the medicinal solution 104. In the upside-down positioning, the piston 108 is moved in a direction where the piston is pushed into the outer tube 109 to transfer the air 103 in the syringe 101 alone into the vial 102 so that the internal pressure of the vial 102 is back to normal. When these steps are repeatedly performed, the medicinal solution 104 in the vial 102 can be aspirated into the syringe 101 with no sharp drop of the internal pressure of the vial 102.
In the case where the air is overly transferred from the syringe 101 into the vial 102, however, the internal pressure thereof increases over a regular pressure, exerting an action to make the vial 102 draw apart from the syringe 101. Such an overly high internal pressure of the vial 102 possibly causes the medicinal solution 104 to flow out from the high-pressure vial 102 into the atmosphere when the injection needle 106 is removed from the rubber cap 107 of the vial 102, which is generally called “aerosol phenomenon”. The aerosol phenomenon is a factor which invites unfavorable events, for example, the medicinal solution 104 may be spilt around, the scattered medicinal solution 104 may be adhered to human body, and the vaporized medicinal solution 104 may be inhaled. To prevent such unfavorable events from happening in view of safety, it is necessary to completely avoid the aerosol phenomenon. Therefore, it is necessary to stop the transfer of the air from the syringe 101 before the internal pressure of the vial 102 becomes too high.
As described so far, the internal pressure of the vial needs to be properly adjusted to avoid an overly high or low internal pressure when the medicinal solution is aspirated from the vial, which is a medicinal solution container, into the syringe. The pressure adjustment should be similarly performed when the medicinal solution is injected from the syringe into the medicinal solution container. Conventionally, it solely relied upon the sensation felt with hands and visual confirmation by an operator who is holding a piston or a plunger to detect the internal pressure of the medicinal solution container. The operator has to manipulate the piston of the syringe while sensing the internal pressure of the medicinal solution container (from negative pressures to positive pressures), which requires a high level of concentration. In large healthcare facilities, for example, it is desirable that as many medication dispensing operations as possible be performed immediately before administering medications in order to improve a time efficiency and also promptly respond to any prescription changes. However, it is a very demanding task to perform the dispensing operation, which requires a high level of concentration, over long hours.
The Patent Document 1 discloses an infusion solution transfer device configured to move a piston provided in a syringe by applying a load thereto using a motor while detecting the internal pressure of the syringe to automatically transfer an infusion solution to a patient. The device developed to inject the liquid solution contained in the syringe into human body is, however, mostly used to check whether the solution is normally transferred. Therefore, the infusion solution transfer device disclosed in the Patent Document 1 can only detect the pressure when the piston is moved to be pushed in. The infusion solution transfer device disclosed in the Patent Document 1 is not configured to move the piston to be pulled out which is an indispensable operability in the dispensing operation or detect the internal pressure of a medicinal solution container when the piston is thus moved. During the described dispensing operation, the operator conventionally holds the syringe with one hand, while holding the medicinal solution container with the other hand. The device disclosed in the Patent Document 1 is a desktop device, which is not designed to be handled with hands. In view of at least these technical disadvantages, the device disclosed in the Patent Document 1 fails to teach any distinctive means effective for supporting the dispensing operation using the syringe.